[linux-lvm] LVM Merge

[Tom Jay]

Hello,

I've posted a question to the debian-user mailing list, but am yet to receive a response.

I am running Debian 7.9 64-bit with kernel version 3.2.0 and would like to use the 'lvconvert --merge' feature, but do not have 'snapshot-merge' support in the kernel. Does anyone have any idea how to enable this?

The original post is here: https://lists.debian.org/debian-user/2016/05/msg00496.html.

Thanks!

Tom

[Alasdair G Kergon]

Post by Tom Jay
I've posted a question to the debian-user mailing list, but am yet to receive a response.
I am running Debian 7.9 64-bit with kernel version 3.2.0 and would like to use the 'lvconvert --merge' feature, but do not have 'snapshot-merge' support in the kernel. Does anyone have any idea how to enable this?
The original post is here: https://lists.debian.org/debian-user/2016/05/msg00496.html.

So you don't have any snapshot support in your running kernel.
But your kernel is modular, and if you attempt a snapshot operation,
lvm2 will try to load the snapshot module if it is available.

To try this manually, do 'modprobe dm-snapshot' (see 'man modprobe')
then retry 'dmsetup targets'.

Alasdair

[Zdenek Kabelac]

Post by Alasdair G Kergon

Post by Tom Jay
I've posted a question to the debian-user mailing list, but am yet to receive a response.
I am running Debian 7.9 64-bit with kernel version 3.2.0 and would like to use the 'lvconvert --merge' feature, but do not have 'snapshot-merge' support in the kernel. Does anyone have any idea how to enable this?
The original post is here: https://lists.debian.org/debian-user/2016/05/msg00496.html.

So you don't have any snapshot support in your running kernel.
But your kernel is modular, and if you attempt a snapshot operation,
lvm2 will try to load the snapshot module if it is available.
To try this manually, do 'modprobe dm-snapshot' (see 'man modprobe')
then retry 'dmsetup targets'.

Please always attach version of lvm2 and kernel in use.

Debian version has some local patches for 'modprobe' usage - so maybe check
it 'auto' modprobe works properly in your case ?
(rmmod dm-snapshot - and check if lvcreate -s still works)

Are you build your own kernel - or do you use 'distro' debian kernel ?


Regards

Zdenek

[Zdenek Kabelac]

Hello, This question was in fact answered by the debian-kernel mailing list,
who informed me that the documentation was probably wrong. The kernel does
actually support merging volumes, just the 'dmsetup targets' output only
refers to output from modules that are already loaded, not what is supported.
https://lists.debian.org/debian-kernel/2016/05/msg00186.html. Thanks! Tom

Hi

The issue is - properly compiled 'lvm2' does call 'modprobe' internally.
So if you have failing 'lvconvert --merge' because snapshot-merge module
was not loaded and you will load it by your own modprobe call - then your lvm2
tool is miscompiled (compiled without modprobe support...)

Regards

Zdenek